New Node: Sharpen node

[Zadfar]

This PR adds a new sharpen node to the Raster: Filter category, allowing users to sharpen images using unsharp masking.

Changes made

• Added new sharpen node with three inputs (amount, radius and threshold)
• Implemented sharpen_algorithm() which uses the unsharp mask technique to sharpen images
• Made a new fn for PremultipliedGammaPixel called to_unpremultiplied_channels(), as this was required by both the sharpening algorithm and gaussian blur algorithm

Notes on implementation

• This implementation borrows heavily from how photoshop did unsharp mask (inputs and ranges), i thought this might be more intuitive for users
• I opted to use the gaussian blur in gamma space as this provided the output most similar to unsharp mask tools from other software.
• There is a hard limit on the threshold variable (255), this comes from the maximum constrast difference in 8bit images
• The soft limits of 100%, 50px and 30 for amount, radius and threshold are arbitrary and can be changed if necessary

Part of #912

[cubic-dev-ai]

All reported issues were addressed across 1 file

<sub>Reply with feedback, questions, or to request a fix.

Re-trigger cubic</sub>

[cubic-dev-ai]

All reported issues were addressed across 1 file (changes from recent commits).

<sub>Reply with feedback, questions, or to request a fix.

Re-trigger cubic</sub>

[cubic-dev-ai]

All reported issues were addressed across 1 file

<sub>Reply with feedback, questions, or to request a fix.

Re-trigger cubic</sub>

[TTyChud]

the bug is on 426: from_gamma_srgb_channels() already returns an unassociated Color, so multiplying by original_a writes associated values into an Image<Color and darkens translucent pixels.

suggestion-
*original = Color::from_gamma_srgb_channels(final_r, final_g, final_b, original_a);

[Zadfar]

I have updated the code to handle the new color struct with unassociated alpha 944d00c. This also clears up the other issues in gaussian blur as well.